This invention relates generally to the processing of fossil fuels, and in particular it relates to new and improved methods for the processing of certain fossil fuels such as oil shales, tar sands, heavy oils and coal.
Liquid fuels are an important energy source in many countries of the world not only for economic, but also for national security reasons. At the present time in history, geo-political factors can bear on the availability of useful liquid fuels in those nations which do not have ample fossil fuel supplies and/or the appropriate processing capabilities to convert the particular fossil fuels into liquid forms.
Severe disruptions in the world petroleum supply in the 1970's gave rise to two energy crises in the United States in that decade. Extensive interest was generated in alternate fuel supplies and considerable resources were devoted to various developmental programs involving geo-thermal, solar, and other non-conventional sources, along with an extensive program whose objective was the development of large-scale synthetic fuel operations.
Although the United States contains substantial fossil fuel reserves, its petroleum reserves have been unable to supply its total demand for liquid fuel, and therefore importation of petroleum has been required to meet the domestic demand. When a rising price for petroleum was imposed by those external forces referred to above, significant attention was devoted to the development of non-petroleum fossil fuels such as coals, oil shales and tar sands. It is estimated that the United States contains reserves of these non-petrolerm fossil fuels sufficient to handle the United States' energy needs for at least several hundred years. The problem, however, arises in converting them economically into useful forms for the various applications of hydro carbon-based energy, generally gases and light liquids.
Various technologies have been proposed for extracting liquids or gases from these non-petroleum hydrocarbon-bearing resources and many were known long before the energy crises of the 1970's. In general, the net energy recovery using these technologies have been economically unfavorable in comparison to the economics of conventional petroleum sources, even at the historical price escalations in crude oil which have essentially remained in place since the energy crises of the 1970's.
Certain other countries of the world are in the same type of energy situation as is the United States. They are net importers of petroleum, but possess local reserves of non-petroleum fossil fuels which could supply domestic liquid fuel needs if suitable technology were available.
Non-economic considerations may also come to bear on the development and expansion of fuel resources, including not only conventional fuel sources, but also non-conventional ones. A specific example is the case of nuclear energy where the consequences of uncontrolled exposure to large doses of nuclear radiation are well-documented.
Nuclear energy has the potential for freeing certain types of energy generation from dependence on liquid or hydrocarbon fuels. For example. nuclear power can be used in place of oil, gas or coal for firing an electric generating plant.
Environmental concerns about the use of nuclear energy, whether legitimate or otherwise, have retarded the domestic expansion of nuclear energy, and today it is not unreasonable to express fear that further significant development of nuclear-electric power facilities will take place very slowly in the United States.
While at the present time in history there are ample supplies of petroleum and other energy sources, there is no guarantee that this favorable situation will continue. Indeed, the United States continues to be dependent upon imported petroleum to a very significant extent. Any future disruption in petroleum imports will create consequences similar to or even more serious than those experienced in the decade of the 1970's.
The technologies which have been proposed for the development of alternate liquid fuel sources, meaning nonpetroleum based resources, take many forms. There is extensive technology on the processing of oil shale and tar sands to extract useful hydrocarbon products. Ther is also substantial technology on the creation of synthetic fuels.
In general it is fair to say that the net energy recoveries from these technologies is such that at today's economics, they are prohibitive to commercial exploitation in a free market.
A representative technology for extracting useful liquid hydrocarbons from tar sands and oil shales comprises subjecting these naturally occurring raw materials to substantial levels of heat and pressure so that as a consequence liquid fractions are obtained. In the case of shale, crushing may be required.
Where such naturally occurring materials are present in ample amounts near the earth's surface, conventional mining procedures can be used to obtain them. Where this is not the case it is necessary to use in situ exploitation with its attendant procedures.
In any event, as noted above, it is fair to say that the net energy recovery using known technologies is not competitive with the present day economics of petroleum.
While it is hoped that the future course of history will not occasion any new energy crises, it is a known fact that the world's recoverable petroleum reserves are finite. Therefore at some point in time it will be necessary to consider alternate fossil fuel sources such as coal, oil shale, and tar sands.
The present invention is directed to a new and improved method for extracting useful hydrocarbons from such fossil fuel resources with a greater net energy recovery than is obtainable using known technologies. Accordingly, the present invention offers significant economic advantage over known technologies because it uses nuclear energy to promote extraction of useful hydrocarbon products from the naturally occurring fossil fuels such as oil shales, tar sands and coal. Stated otherwise, this invention utilizes ionizing radiation applied to the naturally occurring fossil fuel in conjunction with pressure and temperature exposures that are low enough to be reasonable, i.e., cheaper and safer than heretofore used.
In one respect, the present invention obtains its improved efficiency through the use of certain solvents in conjunction with exposure to a certain level of ionizing radiation such as gamma rays, charged particles and neutrons. The usage of solvents in conjunction with gamma irradiation has been shown to have a synergistic effect on the extraction of useful hydrocarbons from oil shales, tar sands, and coal.
In the application of the invention to the processing of oil shale, a preferred procedure for the practice of the invention comprises the use of a hydrogen donor solvent which is driven by the ionizing irradiation to cause extraction of hydrocarbons from oil shale raising the hydrogen-carbon ratio of the extracted material and at the same time eliminate substantial quantities of any sulphur and nitrogen which may be present in the natural shale. The process can be conducted at or near ambient temperatures and pressures so that external energy inputs to the process are minimized and the operating conditions are less demanding and expensive.
The use of hydrogen donor solvents to promote the liquefaction of coal is known. In treatment with heat and pressure, it is believed that there is a transfer of hydrogen from the solvent to the coal and that the hydrogen transfer mechanism is essentially the thermal decomposition of the coal into free radicals. It has been discovered in this invention, as an example, that the donor solvent "n-heptane" possesses synergistic qualities in extraction of hydrocarbon from oil shale when driven by gamma radiation under ambient temperature and pressure. Other donor solvents are also suitable such as the generic groups represented by cyclohexane, tetra hydrofuran (THF) and tetralin.
Others have considered using radiation to promote the extraction of hydrocarbons from tar sands and coal but none have conceived of processes which utilize the donor solvents in combination with the radiation to thus enable the process to be carried out at low temperatures and pressures.
In the case of coal, it has been found that radiation by a gamma source can serve to obtain liquid hydrocarbon products from crushed coal by donor-solvent extraction with the irradiation providing synergistic enhancement.